1. Field of the Invention
The present invention relates to a positive resist composition and a method of forming a resist pattern.
Priority is claimed on Japanese Patent Applications No. 2008-305362, No. 2008-305363 and No. 2008-305364, filed Nov. 28, 2008, the contents of which are incorporated herein by reference.
2. Description of Related Art
In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure of radial rays such as light or electron beam, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film. A resist material in which the exposed portions become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions become insoluble in a developing solution is called a negative-type.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are starting to be introduced in mass production of semiconductor elements. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a wavelength shorter than these excimer lasers, such as F2 excimer lasers, electron beam, extreme ultraviolet radiation (EUV), and X-ray.
Resist materials for use with these types of exposure light sources require lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources. As a resist material which satisfies these conditions, a chemically amplified resist is used, which includes a base resin that exhibits a changed solubility in an alkali developing solution under the action of acid and an acid generator that generates acid upon exposure. For example, a chemically amplified positive resist contains, as a base resin, a resin which exhibits increased solubility in an alkali developing solution under the action of acid, and an acid generator. In the formation of a resist pattern, when acid is generated from the acid generator upon exposure, the exposed portions become soluble in an alkali developing solution.
Currently, as a chemically amplified positive resist, a resin is typically used in which hydrophilic groups are protected with groups which dissociate by action of acid generated from the acid generator (i.e., acid dissociable, dissolution inhibiting groups), and as such resins, polyhydroxystyrene-based resins in which a portion of the hydroxyl groups has been protected with acid dissociable, dissolution inhibiting groups, copolymers of hydroxystyrene and (meth)acrylate esters having an acid dissociable, dissolution inhibiting group (for example, refer to Patent Documents 1 and 2 and Non-Patent Document 1), acrylic resins having an acid dissociable, dissolution inhibiting group (for example, refer to Patent Document 3), or the like are known.
Here, the term “(meth)acrylic acid” is a generic term that includes either or both of acrylic acid having a hydrogen atom bonded to the α-position and methacrylic acid having a methyl group bonded to the α-position. The term “(meth)acrylate ester” is a generic term that includes either or both of the acrylate ester having a hydrogen atom bonded to the α-position and the methacrylate ester having a methyl group bonded to the α-position. The term “(meth)acrylate” is a generic term that includes either or both of the acrylate having a hydrogen atom bonded to the α-position and the methacrylate having a methyl group bonded to the α-position.
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. Hei 8-101509
[Patent Document 2] Japanese Unexamined Patent Application, First Publication No. 2000-267286
[Patent Document 3] Japanese Unexamined Patent Application, First Publication No. 2003-241385
[Non-Patent Document 1] Journal of Photopolymer Science and Technology, Vol. 13, No. 3, (2000), pages 397 to 404
With the expectation of further progress in lithography techniques and further expansion in the potential fields of application for such lithography techniques in the future, there are growing demands for the development of novel materials that can be used in lithography applications. For example, as miniaturization of resist patterns progress, improvement will be demanded for resist materials with respect to resolution. Furthermore, as the resolution improves, improvement will also be demanded for resist materials with respect to other various lithography properties. For example, when the rectangularity of the cross sectional shape of the resist pattern is low, the formation of very fine semiconductor elements or the like may be adversely affected. Accordingly, improvements in the resist pattern shape become more and more important as the resist pattern is miniaturized. In particular, since the lithography processes using electron beams or EUV are targeting the formation of very fine patterns with dimensions of several tens of nanometers, improvements in the resist pattern shape are becoming extremely important.
The present invention takes the above circumstances into consideration, with a first object of providing a positive resist composition capable of forming a resist pattern with a high level of resolution and an excellent shape, and a method of forming a resist pattern.
Further, as a second object, the present invention provides a positive resist composition capable of forming a very fine resist pattern with an excellent shape, and a method of forming a resist pattern.